The present invention pertains to nuclear steam supply systems (NSSS) and, more particularly, to a device for sealing a penetration in a pressurizer for such a system.
In a nuclear steam supply system, the pressurizer maintains reactor coolant system operating pressure and, in conjunction with the chemical and volume control system, compensates for changes in reactor coolant volume during load changes, heatup, and cooldown. During full-power operation, the pressurizer is about one-half full of saturated steam. Reactor coolant system pressure may be controlled automatically or manually by maintaining the temperature of the pressurizer fluid at the saturation temperature corresponding to the desired system pressure.
Typically, the pressurizer is a cylindrical pressure vessel, vertically mounted and bottom supported. A small continuous spray flow is maintained in the pressurizer to avoid stratification of the pressurizer boron concentration and to maintain the temperature in the surge and spray lines. Energy is supplied to the water by replaceable, direct-immersion, electric heaters which are inserted from the bottom head of the pressurizer. A number of the heaters are connected to proportional controllers which adjust the heat input to account for steady-state losses and to maintain the desired steam pressure in the pressurizer.
The individual heaters are carried in tubular heater sleeves which are sealingly attached to the pressurizer pressure vessel. In the event that a leak develops in one of the heater sleeves, means must be available to quickly and effectively seal the leak, to prevent the escape of radioactive water, while the system remains in operation.
It is, therefore, a primary object of the present invention to provide a device for sealing a penetration in a pressurizer for a nuclear steam supply system and, more particularly, a leak associated with a pressurizer heater sleeve.
It is a further object to provide such a sealing device which may be quickly and effectively utilized to seal such a leak while the system remains in operation.
These and other objects and advantages of the invention as may hereinafter appear are achieved by a sealing device including a hollow cylinder adapted to be inserted into the tubular heater sleeve, in place of the heater. The cylinder includes a nose portion formed with a plurality of axially extending slots defining therein a number of radially displaceable segments, each of which has an outwardly extending flange, proximate its distal end, which is engageable with the heater sleeve to resist blowout. A rod, inserted into the cylinder, seals the passage therethrough while locking the displaceable nose portion segments in their sleeve-engaging position.
Advantageously, the cylinder is formed of a nickel alloy and includes an annular band of soft nickel on its external surface which engages the inner surface of the heater sleeve to provide an effective seal therebetween.